1. Technical Field
The present invention relates to a rotary connector used for transmitting an electric signal, optical signal, electric power or the like between a rotary body and a fixed body.
2. Related Arts
A rotary connector is used for electrically connecting a rotary body to a fixed body supporting the rotary body. For example, the rotary connector is used for transmitting an electric signal from the vehicle body to an air bag system or the like mounted in the steering of the car. The rotary connector applied to the car includes an outer case and an inner case which is installed within the outer case in rotatable manner relative to the outer case. A cable housing is formed by thus installed outer case and inner case, and flat cables are received within the cable housing.
The outer case has a bottom portion and an outer cylindrical portion, and the inner case has an upper lid portion and an inner cylindrical portion. The inner case rotates within the outer cylindrical portion of the outer case. In addition, a fixed connecting portion is provided with the outer case, and a rotary connecting portion is provided with the inner case. After one end of the flat cable is connected to the fixed connecting portion, the flat cable received in the cable housing is wound along an inner wall of the outer cylindrical portion in one direction. A winding direction of the flat cable is reversed at a reversing portion, and then the flat cable is wound along an outer wall of the inner cylindrical portion. The other end of the flat cable is connected to the rotary connecting portion. Furthermore, there are proposed that the flat cable is wound within the cable housing in one direction, and that the reversing portion is formed by a roller.
It is required that the inner case is set to be in such a rotational position that the number of possible clockwise rotations of the inner case is the same as the number of possible counterclockwise rotations of the inner case, when the rotary connector is attached to the vehicle body. The above described state is hereunder called as the neutral state.
A fixing tool is arranged to fix the inner case to the outer case in the rotary connector, and the inner case is provisionally fixed by the fixing tool so that the neutral state is maintained until the rotary connector is attached to the vehicle body.
There is proposed that an aligning mark is provided at the respective appropriate locations of the outer case and the inner case so as accurately return to the neutral state of the inner case after removing the fixing tool.
However, the above described marks match even in the situation that the inner case rotates one time. Accordingly, in case that the inner case largely rotates after the fixing tool is removed, the inner case is hardly returned to be in the neutral state.
In particular, when the rotary connector is detached from the vehicle body for repairing after being attached thereto, it is necessary that the inner case is returned to be in the neutral state before being attached again to the vehicle body. Since the inner case is not provisionally fixed by the fixing tool in this case, the inner case is hardly returned to be in the neutral state.
In order to solve the above described problems, Japanese Patent Application Publication No. 2004-222369 discloses that in addition to the aligning mark, a sighting window is provided with the inner case to be able to sight the reversing portion of the flat cable when the inner case is in the neutral state.
The reversing portion moves in a circumferential direction within the cable housing together with the rotation of the inner case. The sighting window is provided at such a location that the reversing portion can be sighted through the sighting window in the neutral state of the inner case. Accordingly, the reversing portion can be sighted through the sighting window only when the inner case is in the neutral state. In other words, the reversing portion cannot be sighted through the sighting window when the inner case is largely deviated from the neutral state.
Furthermore, when more than two flat cables are received in the cable housing, the reversing portion of other flat cable is sighted through the sighting window even when the inner case is not in the neutral state, thus falsely recognizing the situation as the neutral state of the inner case.
Japanese Patent Application Publication No. 2004-222369 also discloses that the aligning marks are largely misaligned when the reversing portion of other flat cable is sighted through the sighting window at the time that the inner case is not in the neutral state. Thus it can be determined that the inner case is in the neutral state when the aligning marks are matched and at the same time the reversing portion of the flat cable can be sighted through the sighting window.
However, a means for recognizing the neutral state of the inner case disclosed in Japanese Patent Application Publication No. 2004-222369 requires to recognize whether the reversing portion of the flat cable can be sighted or not through the sighting window while the aligning marks are caused to be matched, thus it possibly takes time to lead the inner case to be in the neutral state. Furthermore, both of the aligning of the marks and the sighting of the reversing portion have to be performed at the same time, thus being bothersome works.
In addition, in the rotary connector disclosed in Japanese Patent Application Publication No. 2004-222369, it has to be designed in such manner that both of the aligning of the marks and the sighting of the reversing portion are performed at the same time when the inner case is in the neutral state, and on the other hand, the aligning of the marks and the sighting of the reversing portion are not performed at the same time, when the inner case is not in the neutral state, thus the manufacturing process of the rotary connector becomes complex.
The present invention has been made to solve the above described problems in the prior arts, and aims to provide a rotary connector in which the neutral state of the inner case can be easily recognized regardless of the number of the flat cables.